This invention relates to the heading of cartridge cases.
In the manufacture of ammunition cartridge cases, cupped blanks are initially formed from a suitable metallic blank of brass by cupping and drawing operations. Such an operation is specifically detailed in U.S. Pat. No. 2,630,916, which produces a cylindrical tube having a relatively thick bottom and a relatively thin side wall. These drawn cup blanks are subsequently subjected to a series of individual operations which form a finished head on the end of the case, and if desired, a tapered neck and mouth portion on the opposite end. Such a series of forming operations is specifically detailed in U.S. Pat. No. 3,061,908, issued Nov. 6, 1962, to A. J. Duffield for "Metal Forming" incorporated by reference herein as if set forth at length.
Heretofore, various methods called "heading" have been employed in performing the work upon the closed end of the cartridge case. One method employed in the heading of cartridge cases involves the working of the metal at the closed end of the cupped blank by impact flattening and outwardly displacing the metal in the formation of a radial flange about the head. The operation simultaneously forms a closed pocket for a primer. The shaped blank is then subjected to a trimming operation which trims the flange to its ultimate dimensions. The final working of the head includes a separate and individual step of piercing a flash hole through the base of the primer pocket.
Still another prior method of forming a metal cartridge case consists of two steps. First, a flange forming operation in which the metal displaced by the punch is forced outwardly to increase the diameter of the head (any excess flange material may be removed by trimming); and second, the primer pocket and flash hole are separately formed by drilling and reaming operations.
Heretofore, the methods and machines employed in the pocketing operations were of extremely complex and intricate nature, as for example, the machine disclosed in U.S. Pat. No. 3,061,908, which uses a multiple step, closely supported punching operation.
It is apparent that heretofore, regardless of the specific methods and case structures used, the forming of cartridge cases required a number of operations and elaborate machinery to form the primer pocket and the flash hole. In addition, the use of such elaborate machinery requires maintenance and painstaking readjustments in order to accurately perform and control the various operations of heading the cartridge case.
Accordingly, it is the object of the present invention to provide a novel method and apparatus of reduced complexity for forming the primer pocket in the heads of cartridge cases and eliminating internal drilling and reaming operations.
Still another object is to provide a novel method and apparatus for forming the heads of cartridge cases while simultaneously forming a fully finished pocket in the head of the cartridge case.
Other objects and advantages will be apparent in the following description and drawing depicting a partial and sectional plane view of a structure which illustrates an embodiment of this invention.
The invention provides a method of forming a primer pocket in a metallic cartridge case which comprises the step of holding a metallic cupped rough-shaped blank with the center portion of the inside of the base unsupported while forcing an external punch a sufficient distance partially through the base of the blank at a pressure sufficient to form a pocket and cause the base of the pocket to separate to produce a finished primer pocket. The punched hole is preferably partly punched and partly torn so that the wall of the primer pocket has a funnel shape toward the inside of the case. Preferably the rim and the other portions of the head are formed simultaneously with the pocket at a single station.
The invention also provides a new shell case structure (as a result of the new pocket forming method) which comprises a metallic shell case with a partially flared funnel-shaped primer pocket.